If you recently started a keto diet and are getting headaches, brain fog, or mental fatigue, don’t be surprised or overly concerned. You’re likely experiencing some of the common (but not fun) side effects that come with transitioning from a carb (glucose)-based diet to a ketone (fat)-based diet. The good news is that these symptoms for new keto dieters are temporary. Also, there are things you can do to help them go away or to be less bothersome while your body settles into the ketogenic lifestyle. 

What Causes Headaches on a Keto Diet?

When you transition out of a typical carb-heavy diet into a low-carb, moderate protein, and higher fat diet, your body takes some time to adjust. Without significant carb intake, your body is learning how to focus on fat-burning as its primary fuel source. During this time, typically one to two weeks, common side effects are expected due to the carbohydrate restriction of a low-carbohydrate diet. This adjustment period is a lot like detoxing. In fact, you are detoxing from a sugary (glucose) diet loaded with starchy vegetables and other sources of sugar. As such, during the first week, it’s normal to experience a variety of detox-like or flu-like symptoms, commonly called the keto flu. One of the symptoms is headaches, which makes sense if you understand the transition process. 

Low Blood-Sugar Headaches

Your brain is used to being powered by glucose (the product of a high-carb diet) rather than ketones (the product of a higher fat, low-carb diet). When you begin a keto diet, your body continues reaching for glucose, even when it’s no longer available and is instead creating ample ketones for energy. This can cause your blood sugar levels (blood glucose) to drop too low (typically below 70 mg/dL), especially if you are intermittent fasting and, if you’re not yet keto-adapted, can become hypoglycemic. In this case, becoming experiencing hypoglycemia is not cause for alarm. It’s part of the transition. However, since your body isn’t used to it, this new low blood-sugar (no glucose) can briefly add stress to your brain and nervous system, and consequently give you a stress-hormone headache, as well as strong hunger and brain fog. Once your body starts utilizing its ketones rather than glucose, you should find some relief from your headache and begin to experience better energy levels and the known health benefits of staying in nutritional ketosis. 


Notice your weight comes off quickly when you start keto? This is actually water loss. When you’re in the transition stage of keto and using up your stored glucose (glycogen), your body excretes extra water. This is because every gram of glycogen is stored and released with three grams of water. So, as your body rids itself of all its glucose reserves, it also eliminates significant amounts of water (and the bloating that goes along with it). If you aren’t replenishing that water by drinking frequently and plentifully, you’ll get dehydrated—and also perhaps get the headache that accompanies dehydration. (You know hangover headaches? Same idea.)

Electrolyte Imbalance 

Also, when you cut way back on eating carbs, your body makes less insulin. Since insulin’s job is to process the glucose in carbs, when you stop eating carbs, your body needs and thus produces less insulin. With less insulin in your system, your kidneys excrete more sodium, one of the electrolytes that regulate your hydration. This sodium excretion can throw off the balance of other essential electrolytes too, such as potassium and magnesium. This imbalance is one of the main reasons people suffer keto-flu symptoms. If you find yourself getting a headache while on keto, it may be related to sodium loss.

Toxins from Stored Fat

When your body begins to use fat for fuel instead of glycogen, it reaches into your fat stores. But these fat stores also store toxins. As the body breaks down its fat, these toxins are released into your bloodstream, potentially causing headaches, dizziness, and fatigue. 

Menstrual Cycle

There’s a lot of misinformation and anecdotal information about the topic of hormones and ketones, yet what is abundantly clear in the literature is ANY diet that results in rapid weight loss or restricts calories (which some folks do initially on keto to help lower the appetite), will change diurnal rhythm (daily patterns) and signal hormonal changes. It’s also true that drops in insulin levels will directly lower estrogen levels. Most folks today are dealing with estrogen dominance thanks to blood sugar imbalance, stress, exogenous hormone disrupting chemical exposure, poor sleep patterns and blue light/screen time excess, all of which creates hormone imbalance.

How to Stop or Prevent Keto-Related Headaches 

What can you do to help with a keto-related headache? Here are some easy remedies to try. They’re also good ongoing practices for your continued success at keto, headaches or not.

  • Hydrate
    Avoid dehydration. Drink at least half of your body weight in ounces of water throughout the day. For example, if you weigh 150 pounds, you will want to drink 75 ounces of water. On top of this amount, if you drink diuretics such as coffee, increase your water intake by 1-1/2 cups of water per cup of coffee. This will also help to flush out toxins that are released while you’re burning fat stores. Some people look to electrolyte supplements during this time. Bone broth or bouillon is also common. But it’s not required, especially if you heed the next three recommendations. 
  • Salt Your Water
    One easy way to make up for sodium lost on the keto diet (and consequently help keep your electrolytes in balance) is to add a pinch of Himalayan salt to each glass of drinking water. You can also add mineral drops to your water to boost your electrolytes.
  • Eat Enough Fat
    Coming off of a high-carb diet, it may seem counter intuitive to eat so much fat. But getting the right amount of macros (i.e. 70 to 80 percent of your daily calories from fat) is essential to a successful keto transition. It’s also your best bet for counteracting a low blood-sugar headache and managing hunger.
  • Eat Quality/Nutrient Dense Foods
    How can you counteract toxins released from fat loss? Ensure you’re eating enough nutrients (within your macros) and, if necessary, don’t get too restrictive on calories too quickly. You don’t want to lose fat too quickly, as doing so releases more stored toxins. Also, when considering your meal plans, try to pick cleaner foods, which contain no GMOs, hormones, and other toxins, such as pesticides. 

The Final Word

Hopefully we’ve helped clear up your questions, and perhaps your headache. But here’s a quick refresher about keto headaches:

  1. Keto headaches are common during the transition from a high-carb to a high-fat, low-carb diet. They’re also temporary and will subside when your body adjusts to using ketones for fuel.
  2. One way to prevent headaches is to hydrate and add a pinch of Himalayan salt to your water to ensure you’re replacing the sodium lost through keto-related water loss. 
  3. Stick with a “clean-keto” diet as much as possible to avoid adding toxins into your diet. 
  4. Be sure to meet your daily macros (fat, protein, and carbs) to help boost energy and encourage your keto transition. 
  5. Rapid water changes in the female body, whether caused by the diuretic ketogenic diet or otherwise, briefly triggers estrogen to dive and can create hormone imbalance, which can lead to headaches. To avoid this, consume more salt, hydrate, and in the case of some women, increase complex carbohydrate intake for the short term right before menses. 

Disclaimer: when starting a new diet, it’s always a good idea to get medical advice first, especially if you already have health risks or preexisting conditions. So always ask your health care provider or dietitian before making any major dietary change, including switching to a high-fat diet.

Keto-Mojo is a participant in some affiliate programs and some of the links above will generate a small commission if you make a purchase through a product link on our site. This is at no cost to you and all proceeds go directly to the nonprofit Ketogenic Foundation [501(c)3 pending] to assist with their mission funding education and research into the ketogenic diet and lifestyle. Keto-Mojo in no way profits from these links.



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